'The extension of the high-earner tax rate will only continue to leave New York behind the rest of the nation in economic competitiveness.' — Mike Durant (above), state director of the National Federation of Independent Businesses

Even the agency that City Council Speaker Christine Quinn wants to play Big Brother to the NYPD thinks it’s a terrible idea.

Department of Investigation Commissioner Rose Gill Hearn wrote a letter to the mayoral front-runner yesterday laying out a laundry list of problems with the proposal that would have Hearn’s agency monitor NYPD policies and procedures.

“I do not think this plan is the best course of action at this time,” said the letter, obtained by The Post.

“DOI will follow the law, whatever it becomes. However, I would be remiss if I did not point out that, in my experience, aspects of the bill raise serious concerns and make its implementation unworkable.”

The legislation — which Mayor Bloomberg has said would cause a crime spike and put the lives of cops and the public in danger — “transforms DOI wholly and completely,” Hearn wrote.

“It will tax DOI’s capacity to carry out its exiting enormous obligations to provide oversight to all of the other mayoral agencies, boards, commissions and city vendors.”

Hearn said Quinn’s plan asks DOI to “do things that are very different” from its normal work of investigating municipal corruption.

The new NYPD inspector general would examine police procedures such as stop-and-frisk — as well as the department’s partnerships with other law-enforcement agencies.

Hearn called that “highly irregular.”

She wrote that the IG would be redundant with the work of the existing police oversight bodies, including the Civilian Complaint Review Board and the Commission to Combat Police Corruption — as well as NYPD Internal Affairs.

“The bill in essence is not proposing an IG so much as it creates a mechanism to co-manage, even override, the police commissioner,” Hearn wrote.

Finally, Hearn warned, “the record has shown that DOI is an effective IG for city government, but DOI cannot dictate to the police commissioner how to deploy his resources and people, enforce the law and keep the city safe.”

Bloomberg vowed to veto the IG position — but Quinn said she has enough council votes to override that veto.